The process of preparing optical or ophthalmic lenses begins with an unfinished or semi-finished glass or plastic optical lens. Typically, unfinished optical lens has a front face with a finished polished front surface and back face with an unfinished back surface. By grinding away material from the back surface of the optical lens, the required corrective prescription is generated. Thereafter, the surface having had the corrective prescription imparted thereto is polished. The peripheral edge of the processed optical lens is then provided with a final desired contour. Thereby establishing a finished optical or ophthalmic lens.
It is necessary during these various processing operations to securely block the optical lens in accurate position. This procedure is often referred to as “lens blocking”.
The accuracy of the blocking device directly influences the lens machining accuracy; therefore high accuracy of the blocking device is required.
During the processing operation a desired prism and/or tore may be introduced. The desired prism may be either a prescription prism or a non-prescription prism, for example a thinning prism. The manufacturing of such desired prism and/or tore requires that the lens be oriented in a desired specific orientation with respect to the manufacturing tools. The introduced prism and/or tore requires a very accurate orientation of the semi-finished ophthalmic lens.
Conventionally, the method of blocking a semi-finished ophthalmic lens may comprise for example:
an orienting step in which the semi-finished ophthalmic lens is orientated using an orienting station,
a moving step in which the orientated semi-finished ophthalmic lens is moved from the orienting station to a blocking station, and
a blocking step in which the semi-finished ophthalmic lens is blocked on a blocking station.
The orienting step may comprise placing the finished face of the semi-finished ophthalmic lens on a positioning device, for example three pins, and orienting the ophthalmic lens.
Once oriented, the semi-finished ophthalmic lens must be blocked leaving the unfinished face of the semi-finished ophthalmic lens accessible for the manufacturing tools. Therefore, the conventional blocking method require a moving step in which the ophthalmic lens is moved from the orienting station to the blocking station.
As can be appreciated, the precision of these methods depends greatly upon the accuracy with which the semi-finished ophthalmic lens is moved from the positioning station to the blocking station.
In the past, emphasis has been placed on the precision in the positioning step and blocking step. The moving step has been of a secondary interest.
For this reason also, and despite the use of ultra-precision computer-controlled apparatus, ophthalmic lens generated nowadays are not always errorless.